This invention relates to shield and cable terminations and in particular the interface between connectors and cables.
This invention is particularly concerned with connectors and cables used with computers and data processing equipment, such as data terminals, modems, CRT displays, data printers, multiplexers and memory systems, test instrumentation, telecommuncations equipment and aerospace and avionic systems.
Under regulations promulgated by various governmental agencies, e.g. Federal Communications Commission (FCC) it is now a requirement that noise (radio frequencing and other emissions in the 20 to 200 MegaHertz range) from equipment be below certain levels.
Accordingly, manufacturers of electrical equipment are now very sensitive to any noise leakage from their equipment since they may not be able to sell to the public. Interconnecting cable systems (cable & terminating connectors) between equipment of an electronic system are obviously one source of potential emissions. With experience it has been determined that cables should be shielded to insure a low degree of noise emissions. Typically, cables are shielded using a metal braided sleeve or a metal filled plastic layer supported by a plastic tube (shrinkable or non-shrinkable). However, it has been found that multipin connectors, e.g. D type end panel connectors, where connected to cable must also be shielded in order to cut down on emissions. One way of conventionally attempting to meet the required reduction in connector-cable interface emissions is the soldering of a drain wire between the braided cable shield and the metal connector frame. However, this has not been found to provide sufficient emission reduction.
Another way of providing the attenuation desired at the connector cable interface has been the use of a pressure sensitive adhesive copper conductive tape, e.g., produced by 3M which is wrapped and then soldered to the metal braid of the cable. The 3M tape appears to be copper particles in an adhesive supported by a copper foil. While this will produce the normally desired emission supression results, and is a vast improvement over the soldered drain wire technique, manufacturing costs are high because (1) the method of manufacture is labor intensive and (2) there is a high rejection rate (as much as 30%) as reported by one manufacturer, as cables are destroyed curing manufacture e.g., a careless person soldering will frequently penetrate with a soldering iron the metal braid and injure the cable conductor wires. It has also been found that with copper particle tape, oxidation of the particles occurs rapidly if exposed to the air and thus the once conductive adhesive becomes ineffective as a conductor.
In order to more consistently meet the attentuation (noise suppression) achievable using the soldered copper tape at much lower costs, the present invention provides a new and improved cable-connector interface shielding system which lends itself readily to manufacture.
The new shielding system does not require soldering and thus labor costs and rejections are considerably reduced. It has been estimated, by a cable manufacturer that manufacturing costs on a ten foot shield cable normally selling for $18 to $20 will decrease by a dollar or more. Thus with a cable manufacturer making 3000 cables per week, it is estimated that annual savings will be about $150,000 or more. Obviously, if the entire industry were to adopt the system of this invention savings could easily be in the millions per year.